In many fields of industry and in many types of workplaces, it is common to use hearing protection devices due to excessive levels of noise and sound in the environment. Such a hearing protection device can for example be in the form of a pair of cup-shaped elements which are connected by means of a connecting element, i.e. a headband or a helmet, wherein each cup-shaped element comprises a generally circular or oval sealing ring which is configured to cover an ear of the user. During use, the sealing ring is intended to rest against the head of a user, thereby enclosing the ear. In this way, the sealing ring defines a sealing and makes it comfortable for the user to wear the hearing protective device by distributing the pressure acting upon the user's head through the sealing ring. More precisely, the sealing ring can be designed generally as a cushion, having a covering surface foil which encloses a foam material.
Optionally, the cup-shaped element can be provided with noise-attenuating material, for example foam material which is designed to absorb sound. Also, the cup-shaped element with the sealing ring can be used so as to form a set of headphones or audio ear muffs. There are different kinds of audio ear muffs, e.g. with built-in radio, communication facilities or active volume technology. In such cases, the cup-shaped element accommodates a loudspeaker.
With regard to a hearing protection device of the above-mentioned type, it is important to design it with a high degree of sound attenuation and also with a high degree of comfort so as to allow a user to wear it for long periods of time. It is also important that the hearing protection is durable and is resistant against wear and degradation due to influence from the environment. It can be noted that the above-mentioned sealing ring is an important component in order to achieve these objects. It is particularly important that a hearing protection device of the above-mentioned type, including the sealing ring, can be manufactured in a simple and cost-effective manner.
Hearing protection devices of the above-mentioned type are previously known. As an example, the patent document U.S. Pat. No. 5,970,160 discloses a hearing protection device comprising a sealing ring with a foam material and a shell element.
Furthermore, the patent document WO 97/48296 discloses a hearing protection device which comprises a sealing ring which is manufactured from a foam material, for example polyurethane. The sealing ring is mounted onto a shell element.
In order to provide an efficient manufacturing process of a hearing protection device of the known type, it is also previously known to manufacture the shell from a generally stiff plastic material such as ABS (acrylonitrile butadiene styrene). Furthermore, the hearing protection device can generally be manufactured in accordance with a process involving injection molding of a support element in the form of a generally annular and plate-shaped component which is made for example from PVC or ABS material. Furthermore, a soft cushion having a surface foil made from PVC and enclosing a foam material is used for manufacturing a sealing ring which is configured as a sealing which is in contact with the user during use. This sealing ring is attached to the plate-shaped component by means of, for example, a suitable adhesive material or by means of welding. Finally, the support element is attached to the shell element. In this manner, a complete hearing protection device is manufactured.
A disadvantage with today's technology for manufacturing a sealing ring for hearing protection devices is that it comprises a high number of manufacturing steps and that it is unnecessarily complex, time-consuming and expensive. Furthermore, such sealing rings are manufactured from materials having a negative impact on the environment. Another aspect concerning the use and storage of hearing protector devices with sealing rings made of PVC is the relatively poor temperature resistance. Too high temperatures can result in deformation, affecting the sealing and attenuating properties.
Consequently, there is a continuing need for improved ways of manufacturing such a sealing ring, in order to improve the efficiency of the manufacturing process and to lower the manufacturing costs.